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Chapter 12
The History of Life
Question | Answer |
---|---|
relative dating | a method of determining whether an event or object, such as a fossil, is older or younger than other events without referring to the object's age in years |
radiometric dating | a method of determining the absolute age of an object, often by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope |
isotope | an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass) |
half-life | the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope |
index fossil | a fossil that is used to establish the age of a rock layer because the fossil is distinct, abundant, and widespread and the species that formed that fossil existed for only a short span of geologic time |
geologic time scale | a standard method used to divide Earth's long natural history into manageable parts |
era | unit of geologic time that includes two or more periods |
period | unit of geologic time that lasts tens of millions of years and is associated with a particular type of rock system |
epoch | smallest unit of geologic time, lasting several million years |
nebula | large cloud of gas and dust in interstellar space; a region in space where stars are born |
ribozyme | a type of RNA that can act as an enzyme |
cyanobacteria | bacteria that can carry out photosynthesis |
endosymbiosis | a mutually beneficial relationship in which one organism lives within another |
Paleozoic | era of geologic time (from 544 to 248 million years ago) during which members of every major animal group alive today evolved |
Cambrian explosion | earliest part of the Paleozoic era, when a huge diversity of animal species evolved |
Mesozoic | era during which dinosaurs roamed Earth (from 248 million years ago to 65 million years ago) |
Cenozoic | geologic time period that began 65 million years ago and still continues today |
primate | a member of the order Primates, the group of mammals that includes humans, apes, monkeys, and prosimians; typically distinguished by a highly developed brain, forward-directed eyes and binocular |
prosimian | oldest primate group that includes mostly small, nocturnal primates such as lemurs |
anthropoid | human-like primate |
hominid | a member of the family Hominidae of the order Primates; characterized by bipedalism, relatively long lower limb, and lack of tail; examples include humans and their ancestors |
bipedal | animal that walks on two legs |